1. Field of the Invention
The present invention relates to a steering angle middle point detecting apparatus for detecting a steering angle middle point of a steering mechanism, particularly to an apparatus for detecting the steering angle middle point by judging a state of straight drive.
2. Description of Related Art
In a power steering apparatus for assisting steering force on the basis of a detected result of steering torque exerted on a steering wheel, a steering angle is usually chosen as one of the steering conditions.
Conventionally, as a means for detecting the steering angle, the apparatus with a sensor such as a potentiometer provided on a steering wheel shaft or a rack shaft for detecting movement thereof has been well-known.
In such a steering angle detecting means, when a vehicle goes straight, an output of a sensor is adjusted and determined to be a predetermined output value, thereby a middle point of the steering angle is detected.
In the conventional steering angle detecting means, however, as the output value of the sensor corresponding to the middle point of the steering angle is predetermined, discrepancy is produced between the predetermined output value of the sensor and the middle point of the steering angle for making a vehicle go straight, by reason of aged deterioration of weighted solidity of the steering mechanism of camber, toe-in and the like, and change due to maintenance and repair of the steering mechanism, thereby causing a problem that the middle point is not detected with high accuracy.
Accordingly, in order to solve the aforementioned discrepancy and to detect the middle point with high accuracy, there is a necessity to compensate the output value of the sensor at an interval of specified period or every time maintenance is carried out.